text: Only the CHO+ ions formed from the ionization of carbon compounds are detected. Thus, the non-methane byproducts of the reactions are not detected by the FID. 
  Since every compound goes through the catalyst bed in the reactor, it can alter certain substances that might be harmful or negatively affect the efficiency and durability of the FID into safer forms. For instance, cyanide is catalytically changed into methane, water, and nitrogen.